1. Technical Field of the Invention
The present invention relates to a cooled blade of a gas turbine, and in particular to a structure capable of preventing cracks in peripheral portions of air-transpiration holes provided at a leading edge portion of the blade for shower-head cooling thereof.
2. Description of the Related Art
Since the stationary blades and the moving blades of a gas turbine are exposed to a high temperature gas resulting from combustion, it is necessary to cool the interior of the blades. To this end, cooling air passages are provided inside of the blades and cooling air is forced to flow through the cooling air passages to cool the interiors of the blades. FIG. 4 is a perspective view showing a conventional cooled blade of a gas turbine. Referring to the figure, a cooled blade 11 has a leading edge 12 and a trailing edge 13. As can be seen, a number of air-transpiration holes 14 formed in the leading edge portion 12 of the cooled blade 11 blowout the cooling air from the cooling air passage formed inside of the blade to thereby effect so-called shower-head cooling.
FIG. 5(a) is a sectional view taken along line C--C in FIG. 4, and FIG. 5(b) is a sectional view taken along line D--D in FIG. 4. In these figures, a plurality of air-transpiration holes 14 provided in the leading edge portion 12 of the cooled blade 11 for shower-head cooling are shown in detail. The cooling air flowing through a cooling air passage 15 formed inside of the blade is blown out to the blade surface by way of the air-transpiration holes 14 to shower-head cool the blade surface.
As is shown in FIG. 5(b), each of the air-transpiration holes 14 is formed with an inclination relative to the blade surface at the leading edge portion 12. The cooling air blown out of the air-transpiration holes 14 is forced to flow along the blade surface due to such inclination of the air-transpiration holes 14, whereby effective cooling of the blade surface can be achieved.
However, as a result of the oblique disposition of the air-transpiration holes 14 relative to the leading edge 12, acute-angled portions 30 are formed between the blade surface and the air-transpiration holes 14 at inlet/outlet ports thereof. In the blade structure having the acute-angled portions 30 mentioned above, thermal stress taking place around the air-transpiration holes 14 will tend to concentrate at the acute-angled portions 30, creating a problem in that cracks are likely to occur around the air-transpiration holes 14.